In the manufacture of glass fibers precious metal containers called bushings or feeders or spinnerets (hereinafter referred to as bushings) are used to form the glass fibers. The bushings are typically provided with a plurality of holes in the bottom sized such that, with appropriate pulling speeds applied to the fibers as they are formed from molten glass flowing through them from the bushing interior, glass fibers of any desired diameter may be produced. The molten glass flowing from the bushings is usually supplied from a forehearth connected to a glass melting furnace or in some instances from the upper part of a marble melt bushing. A typical marble melt bushing is shown on pages 101 and 102 of the book "The Manufacturing Technology of Continuous Glass Fibers", by K. L. Lowenstein, Elsivier Publishing Co. N.Y. 1973. A typical glass melting furnace, associated forehearth and the bushings attached thereto is shown on pages 61-63 of the same book. The holes in the bushing have tips or nozzles (hereinafter tips) depending from them and they are formed by various methods of manufacture. A description of the function of the tips and their methods of manufacture is provided on pages 89-99 of the above referred to Lowenstein text.
In constructing bushings and the tips used on them the metal used must be one which is substantially inert to molten glass which, during the formation of glass fibers, is constantly in contact with the bushing interior and the tips. The bushings and the tips are thus typically fabricated from precious metals and alloys thereof. In general platinum and alloys of platinum are used for this purpose with platinum-rhodium alloy being preferred. The rhodium content of this preferred alloy is usually 20 percent by weight of the alloy, with the balance of the weight being platinum.
As will be appreciated, the use of precious metals introduces into the fiber glass manufacturing art considerable costs even though the precious metals are not lost during the manufacture of the glass fibers to any appreciable extent. Thus the normal bushings used in glass fiber manufacture, besides having a bottom tip plate, are provided with side walls and electrical connectors built into them that require welding to the bottom tip plate in the assembly thereof. The tips from which the glass fibers form are typically coined and deep drawn from the tip plate. These forming operations introduce fabrication steps that are time consuming and expensive. They also add considerably to the cost of the fiber forming operation in general.
For the above reasons, therefore, a need exists in the art to provide for simpler bushing constructions that will result in a shortening of the normal fabrication times required to construct a production bushing. Still further, the need to reduce substantially the quantity of precious metal used in a given bushing also exists.
By virtue of the instant invention, a bushing is provided which uses a precious metal plate for the tip section. The bushing further is one which substantially reduces the normal precious metal requirements of a glass fiber forming bushing of a given size over that which would normally be required. Fabrication costs for bushings constructed according to the invention are also reduced substantially. The invention, therefore, provides the art with a much sought after goal of substantially reducing the large capital investment in precious metals currently needed to sustain a modern fiber glass production facility while also reducing labor costs.